A communications system, particularly one connected to a publicly accessible network, generally has flaws that can be exploited to render all or portions of the system unusable. For example, a Denial of Service (DoS) attack is designed to flood a target packet network or device with traffic in order to render the target unusable by legitimate users. Such attacks may be based on exploiting a vulnerability in the system (e.g., a limitation in a network protocol such as TCP/IP) or may be based on exhausting system resources. In the latter case, the amount of traffic is intended to overwhelm the target and prevent the target from handling legitimate traffic. For example, if a user attempts to contact a server that is the target of an ongoing DoS attack, the server may be overwhelmed by the traffic and unable to respond to the user's request. Such attacks frequently disable the target until the attack ends, and may be launched against a variety of services, including voice-over-IP (VoIP), instant messaging, and other packet based services. DoS attacks may even be targeted against a particular user of a system if certain information about the user (e.g., VoIP phone number or instant messaging user name) is known.
Accordingly, what is needed is an improved system and method for addressing these issues.